Method of pumping explosive slurry

ABSTRACT

The invention is to a method of filling bore-holes by pumping an explosive slurry by a primary pump through a hose more than 50 ft. in length to a secondary unit in a restricted underground space. From the secondary unit the explosive slurry is pumped through a hose inserted in a borehole and an additive is pumped into the explosive slurry. Control devices for controlling the flow of explosive slurry are provided.

Unite States Patent [1 1 Williams et al. Nov. 6, 1973 METHOD OF PUMPINGEXPLDSHVE 1,038,806 9/1912 Welcker 302/12 SLURRY 3,380,333 4/1968 Clayet al.... 86/20 C 3,523,048 8/1970 Hopier, Jr 149/44 X [75 inventors:Darrell Andrew Williams, West Heidelberg; Adam Prus Wisinski, Parkdal?both of Vlctona, Primary Examiner-Leland A. Sebastian Australla AttorneCushman, Darb & Cushman y y [73] Assignee: ICI Australia Limited,Melbourne,

Victoria, Australia [57] ABSTRACT [22] Filed: July 24, 1972 21 APPL 274430 The invention is to a method of filling bore-holes by pumping anexplosive slurry by a primary pump through a hose more than 50 ft. inlength to e second- [30] Forelgn Apphcamm Pnonty Data ary unit in arestricted underground space. From the Aug. 16, 1971 Australia 5915ondar unit th xplosive lurry is pumped through a hose inserted in aborehole and an additive is pumped [52] C 8 into the explosive slurry.Control devices for control- 302/12 ling the flow of explosive slurryare provided. [51] Int. Cl. F42d l/00 [58] Field of Search 86/20 C;302/12 [56] References Cited 4 Claims, 2 Drawing Figures UNITED STATESPATENTS 827,296 7/1906 Donnelly 302/12 STATlC MIXER PATENTEDHUV 6 i975PR\MARY PUMP CONTROL LINE SLURRY HOPPER SLURRY PUMP STATK: MIXER 1METHOD OF PUMPING EXPLOSIVE SLURRY This invention relates to a methodand apparatus for the manufacture and use of slurried explosives inmining operations.

Slurried explosives normally comprise at least one oxygen releasing saltselected from the group consisting of inorganic nitrates, andperchlorates and mixtures thereof, a thickening agent, a fuel and water.Optionally additives, for example agents increasing sensitivity and fuelcontent, may be added.

Usually the oxygen releasing salt is chosen from the nitrates of thealkali metals or ammonium such as ammonium nitrate and sodium nitrate.The amount of oxygen releasing salt is not narrowly critical;compositions containing amounts of oxygen releasing salts from 50% w/wto 90% w/w of the total composition are satisfactory. The particle sizeand'shape of the oxygen releasing salt is not critical and is well knownfrom the art of ammonium nitrate manufacture; powders and prilledparticles are satisfactory.

The nature of the fuels in such compositions is determined by therequirements that they burn in the presence of oxygen or an oxygencontaining gas and that their physical nature is such that they may beincorporated in such compositions in a manner so as to be substantiallyuniformly distributed throughout the compositions. Such fuels arewellknown in the art and they may be organic or inorganic and may also bederived from animals and plants.

The fuels employed in such compositions can be, for example,self-explosive fuel, non-explosive carbonaceous fuel, non-metallic andmetallic fuels or mixtures of the aforementioned types of fuels. Theycan be varied widely provided that, in the composition in which anyparticular fuel is used, the fuel is stable, that is, prior todetonation, during preparation and storage, the fuel is chemically inertto the system. Examples of selfexplosive fuels include one or moreorganic nitrates, nitro compounds and nitramines such astrinitrotoluene, cyclotri(or tetra)-methylene tri(or tetra)nitramine,tetryl, pentaerythritol tetranitrate, explosive grade nitrocellulose andnitro-starch.

The self-explosive fuel can be for example in any of the well-knownflake, crystalline orpelleted forms. In general up to 35 percent andpreferably from to 30 percent by weight based on the weight ofcomposition of self-explosive fuel is used.

Suitable water soluble fuels are organic water soluble substances, forexample urea, carbohydrates such as sugars or molasses, water solublealcohols or glycols, glues or mixtures of these. The proportion of watersoluble fuel in such compositions should be at least 0.8% w/w and may beas high as 8% w/w of the total composition. v

Suitable water insoluble or sparingly water soluble fuels may be chosenfrom inorganic materials for example sulphur, aluminium, silicon,magnesium, titanium, boron, mixtures thereof and mixtures of aluminiumwith ferro-silicon or organic materials for example finely dividedcharcoal, anthracite, gilsonite, asphalt, cellulosic materials such assawdust, or cereal products for example flours, dextrins or starches.When the inroganic fuel is a metal it is preferably in powder formranging in particle size from very fine, for example a powder passing a200 B.S.S. sieve, to coarse, for example a powder retained on a 30B.S.S. sieve. ln particular aluminium powder passing a 300 B.S.S. sieve,for example paint fine aluminium, may often be used with advantage as afuel; it also acts as a sensitiser. The propor tion of water insolubleor sparingly water soluble nonmetallic fuels in such compositions isusually in the range from 1% w/w to 10% w/w of the total composition.The proportion of metallic water'insoluble fuels, such as aluminium,when present in such compositions may be as high as 25% w/w and amountsin the range from 1% w/w to 15% w/w of the total composition are usuallypreferred.

The proportion of water in such compositions should be suffiicent todissolve at least part of the water soluble fuel when present, and partof the oxygen releasing inorganic salt, say from 5% w/w up to 35% w/w,but not be in excess of the explosive limit of the composition.

Many thickening agents (viscosity raising agents) are known which havebeen employed with varying degrees of success, either alone or incombination, in waterbearing explosive slurries. Amongst these may bementioned galactomannan polysaccharides such as guar gum, Tara andPaloverde gums, pregelatinised starches, hydroxyethylcellulose,carboxymethylcellulose, tamarind seed flour and hydrophilic vinylpolymers such as polyacrylamide. The most widely used of thesethickening agents have been the galactomannans, particularly guar gum.

When compositions comprising polysaccharides such as guar gum are mixedwith appropriate crosslinking agents, the viscosity of the compositionis increased. Any of the known crosslinking agents conventionallyemployed for galactomannans can be used including potassium and sodiumdichromate, sodium tetraborate, borax, certain transition metal saltsand certain soluble antimony and bismuth compounds. However, alkalimetal dichromates, for example sodium and potassium dichromates, areespecially preferred.

The proportion of polysaccharide and conventional crosslinking agentused in preparing 'the thickening agent component of the viscousslurried explosives can vary over quite wide limits depending on theagent used as is well known in the art. For example, using-guar gum withzinc chromate as the crosslinking agent the proportion of guar gum mayvary from'0.l to 5% w/w of total composition and the proportion of zincchromate may vary from 0.01 to 3% of total composition.

Alternatively a mixture of sodium or potassium dichromate and a solubleiron, zinc, aluminium or antimony salt may be used. For example ifsodium or potassium dichromate is used the proportion of sodium orpotassium dichromate in the viscous slurried explosive should be in therange from 0.003 to 0.9% w/w, the proportion of soluble salt should bein the range from 0.001 to 0.3% w/w of the viscous slurried explosive.

There are many alternative combinations of free flowing materials whichwill on mixing give a viscous crosslinked slurried explosive.

, Explosive slurries may also be thickened by viscosity raising agentsformed from the in situ polymerisation of monomers or mixtures ofmonomers. Examples of monoethylenically unsaturated. monomers which aresuitable include amides such as acrylamide, methacrylamide andN-methylacrylamide and hydroxyalkyl derivatives such asalpha,2-hydroxyethylacrylamide and alpha-hydroxymethylacfylamide; acidssuch as acrylic acid and methacrylic acid; salts of acrylic acid such assodium, potassium or ammonium acrylate; and soluble salts ofmonovinylpyridines, particularly and preferably the nitrate salts of the4-vinylpyridine. Acrylamide is a particularly preferred monomer becauseof its low cost and rapid polymerisation in the presence of free radicalpolymerisation promoters in the aqueous phase of the blastingcompositions. Usually, the concentration of acrylamide used ranges from0.3 to 10 percent and especially from 0.5 to 5 percent. Suitablepromoters include sodium, potassium and ammonium salts of inorganicperacids such as persulphates, perborates and pervanadates; hydrogenperoxide and organic peroxide and azo catalysts such asazobis(isobutyronitrile),alpha,alpha'-azobis(alpha,gamma-dimethyl-gammamethoxyvalero-nitrile), tertiary butylhydroperoxide, methylvinyl ketone peroxide, benzoyl peroxide andperacetic acid. Persulphates are usually preferred. Redox systems, thatutilise a source of persulphate ion (S,O ').as one component; aresuitable throughout a range ofconcentrations of inorganic persulphatesalt; can be used alone in the solution of inorganic oxidising salt topromote the copolymerisation reaction or an added reducing agent canalso be employed to form a redox couple. Reducing agents that can alsobe used if desired include nitrogen bases such as hydroxylamine,carbohydrazide and, particularly, hydrazine. If needed, higher rates ofpolymerisation are achieved at lower temperatures when thepolymerisation system also includes a minor amount of metal ion, usuallya Group [B metal ion; These metalions' 'are introduced as solubleinorganic or organic salts, e.g. as the nitrates, sulphates or acetates.Other useful persulphate couples are I-ISO- (S2Og) and Fe -(S2O and SgO(S2Og) and nitro-tris-propionamide -(S O In general, the total amount ofpromoter used varies with the particular. promoter and monomers, andincreases proportionately with the desired speed of polymerisation, butusually is at least 0.002 percent and preferably within the range ofabout from 0.002 to 3 percent based on the total weight of aqueous phasecontaining monomers to be polymerised, large excesses of promoter havingno detrimental effect on the gel structure. The optimum concentration ofthe preferred persulphate ions, based on total monomers, i.e. bothmonoand polyethylenically unsaturated, can vary considerablydepending'on the particular polymerisation system, the desiredconsistency of the gel, and the presence or absence of supplementarypromoter components, but in general will be about from 0.005 to 2percent by weight of'the aqueous phase.

In the past slurried explosives have been widely used in miningoperations. Their major commercial use has been in open cut extractionof minerals but bulk loaded slurried explosives have not been used toany great extent in underground mining operations.

Packaged slurried explosives have been used in underground miningoperations. Thus cartridge cases may,

be filled with slurried explosives in a factory anditransported to themine for use. The cartridges'are, pushed into the borehole manually butit is difficult; to ensure that the borehole is completely filledandtherefore they are not reliable in use. Packaged slurried explosivesare expensive and have none of the economies inherent in the use of bulkloaded slurried explosives. Bulk loaded slurried explosives are cheapand readily available and therefore it is surprising that they have not;been used widely in underground operations. The main reason for thislack of use resides in the fact that minimised. In addition the slurryis normally prepared and pumped at an elevated temperature so as todecrease the viscosity of the slurry.

This solution to the problem is not convenient for use underground assuch operations must be carried out in the restricted spaces inherent inunderground mining operations and it is difficult to provide supplies ofthe slurry raw material to the working area and also to find space atthe point of use to fit in the large mixing and pumping unit required inthe manufacture and use of explosive slurries.

The handling and manufacture of explosive slurries underground ishazardous especially if high temperatures are used to reduce theviscosity of the slurry. Boreholes in underground mining are often 300or more feet away from the nearest point of access for heavy machineryso that even ifthe explosive slurry was prepared at'a high temperature,the temperature would fall by the time the slurry was pumped to thepoint of use.

A further difficulty in using explosive slurries underground is that theboreholes normally used underground are of a much smaller diameter thanthose used in open cut mining.

Small boreholes are used in underground mining operations becausefirstly, it is difficult,-and often impossible, to carry the large andheavy machinery required for boring large holes in the restrictedpassages adjacent to the working area and, secondly, because inunderground mining there is a need for much greater control of blastingpower to prevent ore dilution or excessive ground vibration leading touncontrolled collapse of the roof of the mine passages.

The viscosity of explosive slurries suitable for use in long upwardlyinclined boreholes is much greater than that required for the downwardlyinclined boreholes normally used in above ground operations.

In downwardly inclined boreholes suitable explosive slurries need onlyhave sufficient viscosity to prevent or reduce seepage of waterdesensitising the expolsive charge. In upwardly inclined boreholessuitable explosive slurries must in addition have sufficient viscosityto remain in place in the borehole. The required increase in viscosityof the explosive slurry also increases the shearing forces generated inthe slurry when the slurry is manipulated by, e.g. pumping.

We have now found means whereby explosive slurries can be manipulatedand used in restricted spaces.

Accordingly we provide an apparatus comprising in combination a primarypump adapted to .deliver explosive slurry through a hose more than 50 ftin length, connected to a secondary unit and a means of adding anadditive to the slurry at, or after, the secondary unit.

We also provide a method of preparing a suitable ex-' plosive slurry foruse in underground workingin restricted spaces which method comprisespumping explosive slurry through a hose to a secondary unit 10- cated inthe restricted space and thence pumping the mixture to a boreholewherein an additive is added to the slurry at or after the secondaryunit.

By secondary unit we mean a unit providing in combination a portablesecondary pump and a portable buffer storage tank. Preferably thesecondary unit is either of suitable dimensions and weight to be carriedmanually into the restricted areas without dismantling, or may bereadily dismantled into easily portable sections and readily reassembledin a restricted area. We have found that it is often convenient toarrange the secondary unit so that it can be readily dismantled into aslurry pump section, a storage hopper section and additive tank and pumpsection.

The additive may be added to the slurry by any means known in the art.For example it may be added at the secondary unit or it may be injectedinto the hose leading from the secondary unit into the borehole. Weprefer that the additive is pumped through a separate hose and mixedwith the explosive slurry immediately prior to delivery of the slurryinto the borehole. Preferably the means of adding the additive comprisesan additive tank, the contents of which may be pumped via an additivepump through a separate hose to the end of the explosive slurry hose.

Preferably there is a means of automatically controlling the primarypump by the height of slurry in the slurry hopper of the secondary unit.The primary pump is automatically stopped when the hopper is full andrestarts when slurry is removed from the slurry hopper.

Preferably the secondary unit is controlled by a remote control devicewhich can be operated by an operator standing near the borehole to befilled. The advantage of using such a remote control device is that oneoperator may control the insertion of the hose into the borehole andalso control the pumping of slurry into the borehole.

As a safety measure we prefer that a detonation trap is inserted betweenthe bulk tank and the secondary unit. Suitable detonation traps are wellknown and include air voids or constrictions in the hose leading fromthe bulk tank to the secondary unit.

After use the slurry remaining the secondary unit and in the hoseleading from the primary pump to the secondary unit may be returned bymeans of air pressure applied to the secondary unit. Thus using oursystem substantially all the explosive slurry prepared is used and largeamounts of, difficult to dispose of, formed, highly viscous, sensitised,waste slurry are not encountered.

Preferably the additive is pumped in a separate stream into the boreholeand mixed with the explosive slurry at the end of the hose carrying theexplosive slurry into the borehole. Thus the additive and the slurry maybe pumped into the borehole thorugh two separate hoses.

We prefer to encase the hoses carrying the separate streams of materialin an outer casing or hose. In our preferred embodiment the hosecarrying the major component of the product is used to encase the hosessupplying the streams of the minor components of the product.Alternatively a single hose may be used comprising two or more conduits.

The means of mixing the streams of material to form the product is anymixer of such dimensions that it can be inserted into the void when themixer is attached to the end of the means for supplying the separatestreams of materials.

Preferably the mixer is of the type known in the art as an interfacialsurface generator mixer. Such a mixer is characterised by having nomoving parts, but the mixer comprises a plurality of interfacial surfacegener ators. It is also characteristic of such mixers that they may bemade in any suitable external diameter. A suitable mixer, for example,is the Static Mixer manufactured by the Kenics Corporation of the U.S.A.

When the apparatus is used to fill boreholes with a slurried explosive,ideally the hose and mixing means should be withdrawn from the hole at,or approximately at, the rate at which it is being filled; however, itis, of course, impossible to observe the rate of charging visually andrecourse must therefore be taken to indirect control, such as empiricaloperation or attempts to synchronise the linear rate of withdrawal withthe linear rate of filling calculated from the pumping rate. As a rulethis is a coarse approximation only and often maloperation results; ifthe hose is withdrawn too slowly it becomes embedded in the material andis likely to leave a columnar gap or cavity on being withdrawn or mayeven be permenently embedded in the slurry by excessive friction orblockages. Conversely, if the hose is withdrawn too rapidly, thematerial is likely to be dropped from a height above the rising surfaceof the slurry and entrap pockets of air or water. In most of theseoperations, discontinuity in the material filling of the hole isundesired or detrimental for the intended purpose.

Yet another problem is that boreholes frequently contain substantialquantities of water. lSlurried explosives dropped or pumped into suchholes may be adversely affected by excessive dilution; for instance, theblasting agent mixture may not be initiated by a detonator or theexplosion may fail to propagate through the mixture.

These difficulties may be overcome by use of a withdrawal apparatus.Withdrawal apparatus is defined as apparatus comprising a tube which issealingly connected to the smaller opening of a truncated conical mantlemade of a material sufficiently rigid or reinforced to be incapable ofinversion, which mantle is mounted coaxially with, on and around saidtube ator near its lower end and the wider opening of which mantle isnearer to the bottom end of said tube, and a flexible hose connectingthe inlet end of said tube to the mixing means. The tube is eithersealingly attached to the mixing means or may itself be the outer caseof the mixing means.

The purpose of the truncated conical mantle is to seal the hose againstthe wall of the borehole; thereby the cavity into which the blastingagent is being discharged is sealed, ingress of water into it isminimised and the fluid discharge pressure of the pump is exertedagainst the enclosed end of the hole thus producing upward thrustagainst the seal formed by the hose and the surrounding truncatedconical mantle. Consequently the pump pressure aids or effects theraising of the hose synchronously with the rate of charging.

Preferably said conical mantle can be folded axially, downwardly but notupwardly towards the axis of said tube, so as to envelop it at leastpartly; in this folded down position, not unlike an inverted, folded-upumbrella, said assembly of tube and mantle may readily be inserted intothe hole and subsequently on withdrawal of the hose the mantle isunfolded into its conical shape.

The material of construction of the mantle is not critical, but it mustbe strong enough to withstand upward thrust into the cone of up toseveral hundred pounds without collapsing, without being invertedupwardly and without tearing; its ability to resist upward inversion iscritical and determines the choice of material, its thickness and itsreinforcement. It may be made of rigid material, eg a metal or plasticsheet or, preferably, or flexible material of sufficient thickness, e.g.a rubber or polyethylene terephthalate sheet; preferably the sheet ispretreated to facilitate the operation of folding it downwards,centrally around the tube, e.g. by providing axial folds in the rubbersheet or by making the cone of a number of metal vanes slideable againsteach other and capable of being unfolded into a progressively widercone.

Preferably, also, flexible truncated cones, particularly rubber sheetcones, are reinforced by rods or strips running along the length of thecone in several, say, 2,3, 4 or 6 symmetrically placed positions; thesestrips may be made of particularly strong materials, e.g. spring steeland prevent inversion and expansion of the bottom opening of the conebeyond a predetermined size.

Optionally the larger opening of the truncated cone may be fitted at itswidest (bottom) section with a skirt, which is an extension of thetruncated cone, but is made .of a more flexible material such as rubberor foam rubber sheet and may act as a sealing washer at the walls of thehole between the discharged slurry and any water above it.

The term truncated cone implies that the central angle of the cone is,at all times, less than 180, in practice preferably less than 140 andmost preferably less than 120. The larger, bottom outlet of thetruncated cone, in its fully unfolded position forms a circle orquasicircle having a diameter which approximates the diameter of theborehole, but which is characterised in that it is substantially smallerthan 21, wherel is the length of the conical mantle. By this means theabove stated angles cannot be exceeded. Consequently, the cone can at notime be inverted upwardly without destruction since the'tensile strengthof the sheet resists expansion beyond its maximum diameter; the termtruncated cone includes cones of less regular shapes,

such as bulging cones, bell-like shaped cones or cones of somewhatirregular, quasicircular cross sections, the essential feature ofthecone being that it is capable of enveloping a fluid thrust upwardlyinto it, without folding backward and that, inserted into a cylindricalor quasicylindrical hole, it is capable of forming against the wall ofsaid hole a seal, or a restriction reducing the flow of liquids past it.I

The truncated cone may be sealingly attached to the tube exactly at ornear the lower end of the tube which is to be inserted into theborehole; it may be wired on, or fittedremovably by means of a screw orbayonet fitting; the tube may protrude into the interior of the cone oreven through both the top (small) and bottom (large) opening of thetruncated cone. More than one, say 2 or 3 cones, mounted in series mayalso be used.

Preferably, additionally, there may be a cap closing the bottom (larger)opening of said truncated cone and removable from it by the pressure offluid being discharged from the tube.

The nature of the additive is dependent on the nature of the explosiveslurry. pumped from the tank into the secondary unit.

In general the physical nature of the explosive slurry .will fallbetween two extremes. At one extreme the slurry has adequateviscosityfor use in upwardly inclined holes but will be desensitised bythe shearing forces generated in the hose leading to the secondary unit.At the other extreme the slurry will of of low viscosity so thatsensitivity is not lost by pumping but the viscosity is not sufficientfor use in upwardly inclined holes. ln slurries of the first extreme theadditive required is a sensitizing agent such as e.g. the finely dividedmetal described hereinbefore. In slurries of the second extreme theadditive required is a viscosity raising agent as have been describedhereinbefore.

The explosive slurries used in practice will often fall between thesetwo extremes and thus require the addition of both viscosity raisingagents and sensitizing agents.

The apparatus of our invention will now be illustrated by reference to apreferred embodiment illustrated in FIGS. 1 and 2 wherein FIG. 1 is aschematic plan of a loading system of our invention, and FIG. 2 is aflow diagram of the system.

In FIG. 1 a bulk tank 1 is connected by means of hose 2 to the primarypump 3. The primary pump is connected to the secondary unit 4 throughthe hose 5. Crosslinking agent is stored in the tank 6 and pumped usingthe pump 7 to the static mixer 8 via the line 9. The slurry is pumped tothe static mixer 8 through the hose l0.

The bulk tank 1 is of conventional construction and may either remainoutside the mine or may be located in a main gallery in the mine. Theprimary pump 3, preferably a pneumatically powered pump is controlled bythe air delivery valve 11. The valve 11 is preferably controlled by anautomatic control 12 which automatically cuts off the pump 3 when theslurry hopper .13 is full and starts the pump 3 when the slurry hopper13 is partially empty. Suitable automatic controls 12 are well known inthe art; a convenient control is shown schematically in the figure. Theslurry in the hopper 13 is pumped via the pneumatically driven pump 13to the inline mixer 8 where it is mixed with crosslinking agent from theline 11. The loading hose 10 is fitted with a loading cone 15 and cap16. The operation of the secondary unit may be controlled by an operatorstanding by the unit and manually controlling the rate-of the slurrypump 14 and the crosslinking agent pump 7, however we prefer that thepumps 14 and 7 are controlled by remote control from a point near theborehole to be filled. Suitable pneumatic remote control devices forsuch pumps are well known in the art.

The secondary unit may be readily dismantled into two parts byuncoupling the flanges shown in FIG..]

along the line AB. The two parts may be manually carried and readilyreassembled.

We claim:

1. A method of filling boreholes from a restricted underground spacewhich method comprises pumpingan explosive slurry from a bulk tank bymeans of a primary pump through a hose more than 50 ft. in length from apoint outside the restricted underground space to a secondary un'itsituated in the restricted underground space said secondary unitcomprising a slurry hopper, a secondary pump, an additive tank and anadditive pump; pumping the explosive slurry from the secondary slurryhopper by means of the secondary pump through a hose inserted into theborehole; pumping an additive from the additive tank by means of theadditive pump into the slurry at, or after the secondary hopper; theoperation of the primary pump being con- 9 w trolled automatically bythe level of the slurry hopper sive slurry hose in the borehole. of thesecondary unit, the secondary unit being con- 3. A method according toclaim 1 wherein the explotrolled by a remote control device from a pointadjasive slurry hose encases the additive hose and is termicent to theopening of the borehole; and said secondary nated by an interfacialsurface generator mixer.

unit may be readily dismantled into readily portable 5 4. A methodaccording to claim 1 wherein there is a sections and readily reassembledin a restricted area. detonation trap between the bulk tank and thesecond- 2. A method according to claim 1 wherein the addiary unit.

tive is pumped through a hose to the end of the explo-

1. A method of filling boreholes from a restricted underground spacewhich method comprises pumping an explosive slurry from a bulk tank bymeans of a primary pump through a hose more than 50 ft. in length from apoint outside the restricted underground space to a secondary unitsituated in the restricted underground space said secondary unitcomprising a slurry hopper, a secondary pump, an additive tank and anadditive pump; pumping the explosive slurry from the secondary slurryhopper by means of the secondary pump through a hose inserted into theborehole; pumping an additive from the additive tank by means of theadditive pump into the slurry at, or after the secondary hopper; theoperation of the primary pump being controlled automatically by thelevel of the slurry hopper of the secondary unit, the secondary unitbeing controlled by a remote control device from a point adjacent to theopening of the borehole; and said secondary unit may be readilydismantled into readily portable sections and readily reassembled in arestricted area.
 2. A method according to claim 1 wherein the additiveis pumped through a hose to the end of the explosive slurry hose in theborehole.
 3. A method according to claim 1 wherein the explosive slurryhose encases the additive hose and is terminated by an interfacialsurface generator mixer.
 4. A method according to claim 1 wherein thereis a detonation trap between the bulk tank and the secondary unit.